With the rising life expectancy and elderly population in the US, how to achieve healthy aging and extend health span is a pressing biomedical question with profound social ramifications. A pivotal biological mechanism governing our well-being is the circadian clock, the intrinsic timekeeping device that responds to environmental changes and coordinates bodily functions throughout the 24-h cycles. Accumulating evidence has demonstrated a strong correlation between aging and circadian dysfunctions, particularly attenuation of circadian rhythms such as sleep fragmentation and reduced amplitude of body temperature and circulating hormone cycles. We recently identified a unique group of Clock-Enhancing small Molecules, now dubbed as CEMs, via high-throughput screening. To investigate the potential causal role of clock attenuation in aging, we will address the hypothesis that CEMs can improve aged clocks and age-related metabolic decline. We focus on energy metabolism because it is closely regulated by the clock and aging is associated with significant decline in energy utilization. Three Specific Aims are proposed. Specific Aim 1: Determine the clock mechanism of CEMs in aged mice. Using aged PER2::luc reporter mice, we will determine whether CEMs can enhance the bioluminescence rhythm at tissue and single-cell levels. To understand the molecular mechanism, we will systematically characterize the core clock loops in aged tissues, and dissect transcriptional and posttranscriptional mechanisms underlying CEM-mediated enhancement of aged clocks. Specific Aim 2: Delineate the role of CEMs in age-related metabolic decline. We will determine whether CEMs can enhance energy metabolism in naturally aged mice by molecular and physiological approaches. To define the molecular mechanism of CEMs in energy homeostasis of aged mice, we will screen candidate metabolic regulators for altered expression or activity in response to CEM treatment, and investigate the metabolic regulatory mechanisms by CEMs in aged mice. Specific Aim 3: Identify the cellular networks and direct targets of CEMs. To identify both chronic and acute cellular responses to CEMs in aged mice, we will conduct RNA-seq transcriptome profiling using samples from aged mice treated with CEMs for varying periods. To identify direct targets, we will carry out chemoproteomic studies involving affinity pull-down with biotinylated CEM derivatives. Anti-aging roles of specific cellular pathways and proteins from these studies will be further investigated by pharmacological and genetic approaches. Successful completion of these Aims will address the critical question regarding a causal role of clock attenuation during aging and reveal an exciting efficacy of CEMs in prolonging health span.